This invention relates to fluorescent lamp ballasts and, more particularly, to a unitary ballast structure for starting and operating four fluorescent lamps.
U.S. Pat. No. 2,404,254, dated July 16, 1946 to Short discloses a fluorescent lamp ballast structure wherein multiple coils are mounted on a single core. Such cores can include air gaps as shown in U.S. Pat. No. 2,620,459, dated Dec. 2, 1952 to Sawyer et al.
Ballast structures comprising a separate filament transformer and reactor wound on the same core structure are disclosed in U.S. Pat. No. 3,059,143, dated Oct. 16, 1962 to Sola.
A multiple coil structure wound on a single core for operating four fluorescent lamps is described in U.S. Pat. No. 2,685,662, dated Aug. 3, 1954 to Feinberg et al.
The fluorescent lamp ballast art is highly developed and the most commonly used ballast, particularly for recessed fixture commercial applications, is the two-lamp series-sequence ballast which is generally referred to as a two-lamp rapid-start ballast. Such a ballast is described in detail in U.S. Pat. No. 2,796,554, dated June 18, 1957. In installations where four lamps are utilized in one fixture, it has been customary to incorporate two of these two lamp ballasts in each fixture. An alternative circuit by which four lamps can be operated from a single ballast is disclosed in U.S. Pat. No. 4,006,384, dated Feb. 1, 1977 to Elms et al.